In general, a CRT (cathode-ray tube) can be reinforced with a heat shrink band, e.g., in order to prevent an implosion thereof. This heat shrink band may be made of a belt-shaped steel sheet by bending it to the shape of a side face of the CRT, and then welding both ends with each other to form a frame. Moreover, a metal bracket can be attached to each of the four corners of the heat shrink band by welding. When fixing the heat shrink band to the circumference of the CRT, the heat shrink band can be thermally expanded by heating it at approximately 500 to 600° C., and then the heat shrink band is set to the circumference of CRT and simultaneously cooled quickly. As a result, the heat shrink band may shrink due to such quick cooling, so that deformation caused by air pressure is corrected by the tension of the heat shrink band generated at that time.
Furthermore, it may be problematic that the weight of a heat shrink band is likely to increase in order to provide sufficient tension to rectify the deformation of the CRT caused by air pressure.
For example, a heat shrink band for use in the CRT of 21 inches in diagonal length may weigh about 700 g or more. Moreover, some heat shrink bands can be subjected to about 0-T bending processing, depending on the shape of the heat shrink band, and hence such a heat shrink band would likely utilize a steel sheet which satisfies both strength and processability. Further, it may be problematic that this heat shrink band can develop rust due to a change of temperature and humidity in a room, after the heat shrink band is fixed to the CRT. There may be a possibility that this rust can have a negative influence on the electronic beam of the CRT in addition to a problem of external appearance. However, it is unlikely to apply oil onto the surface of the steel sheet for use in a heat shrink band, in view of its use. Thus, in the heat shrink band, an electric galvanized steel sheet, a melting galvanized steel sheet, a melting zinc-aluminum plated steel sheet, a melting aluminum plated steel sheet, etc. can be used in order to reduce or prevent a formation of such rust.
For example, a use of a zinc type plated steel sheet may be problematic because alloying of zinc occurs may cause a discoloration, in the procedures of heating and expanding the heat shrink band at a temperature of about 500 to 600° C. This discoloration, although only a problem of appearance, may decrease its commercial value significantly. On the other hand, with respect to an aluminum type plated steel sheet, although such steel sheet would likely not discolor upon being heated at a high temperature for a short time such as a high-frequency induction heating, if it is heated by gas at a high temperature such as about 550° C. for a relatively long time period, for example at about 650° C. for approximately 15 seconds or more, then it may become discolored.
Japanese Patent Publication No. 2-61544 describes a production method of a heat-resistant aluminum-surface-treated steel sheet which includes a generation of a fine AlN layer which can prevent counter diffusion of Fe and Al during heating after metal plating, thereby suppressing alloying.
Japanese Unexamined Patent Application, First Publication No. H9-195021 describes a melting aluminum-plated steel sheet which can have a component system, such as a steel component, consisting of a predetermined amount of O and each of Ti, Nb, V, B, etc., in a particular amount so as to maintain sol-N stably, and which is subjected to melting aluminum plating, thereby likely preventing discoloration due to alloying.
Japanese Unexamined Patent Application, First Publication 2003-34844 describes an aluminum-plated steel sheet suitable for processing at high temperature which can achieve high strength after being processed at high temperature, e.g., as a result of adding Ti, P, Ni, and Cu thereto.
Japanese Patent Publication 5-26864 describes a production method of a molten Al-plated steel sheet which excels in gloss retention of the plated layer at high temperature, e.g., a steel sheet having a plated layer which may not discolor even if the steel sheet is used at a high temperature of approximately 550° C., e.g., because a barrier layer made of AlN can be formed at the boundary between the plated layer and steel sheet upon being heated, by leaving free nitrogen after plating. However, since the Si content and Mn content may be small, if the Al content is about 0.02 or less, then deoxidization may become insufficient at the time of exchanging of a ladle during a continuous casting, etc.
Thus, exemplary embodiment of the present invention are described herein which address at least some of the issues associated with a conventional arrangements and/or method. For example, it is one of the exemplary objects of the present invention to provide an aluminum type plated steel sheet which excels in discoloration resistance, and weldability, which may not decorate after re-heating and which can prevent increasing strength, and a heat shrink band that can utilize the same.